M-Factor paste proves decisive for Siemens

Soldering & Surface Mount Technology

ISSN: 0954-0911

Article publication date: 1 April 2000




(2000), "M-Factor paste proves decisive for Siemens", Soldering & Surface Mount Technology, Vol. 12 No. 1. https://doi.org/10.1108/ssmt.2000.21912aab.038



Emerald Group Publishing Limited

Copyright © 2000, MCB UP Limited

M-Factor paste proves decisive for Siemens

M-Factor paste proves decisive for Siemens

Keywords: Siemens, Solder paste, Cobar

Intermittent soldering defects on a control PCB have led Siemens plc of Congleton, Cheshire to assess, and to convert to, Cobar's new M-Factor solder paste.

Siemens' process engineers discovered that bad joints were occuring at random on a QFP144 device. There was no pattern to the occurrence; a good batch of 20 might be followed by three failures in a row. A faulty batch of devices having been ruled out, they decided that the solution might be to increase the activity of the soldering materials.

Having passed Siemens' own laboratory trials, Cobar's 325RXM paste was tested on the production line. The paste produced a noticeably brighter joint, with full wetting apparent from bottom to top of the leads and a reduction in flux residues around the joint. Use of 325RXM paste in conjunction with Cobar's 390RXHT wave soldering flux and Cobarcore no-clean wire has given Siemens the added benefit of fully compatible activator chemistries.

There were also in-process benefits. Stencil life was unaffected by the change, the paste was visibly wetter and the roll characteristics were better. Print definition was flatter over the length of the deposit, with a reduction in "scooping" at the exit of the aperture in the print direction. There was also a major reduction in oven cleaning and maintenance because the Cobar materials are fully synthetic.

Andy Lowe, Siemens' process engineer, says: "The same paste can be used over and over again, with no need to throw it away after batch run. This cuts scrap levels and the volume of paste needed. We choose to throw any remaining paste away after seven days on the batch line, even though it shows no degradation. On the flow line the working paste is only ever topped up; therefore no scrap is produced".

For further inforamtion, please contact: Terry Morgan, Parkheath Ltd, East Moors Business Park, East Moors Road, Cardiff CF1 5JX, UK. Tel: +44 (0) 1222 462230.

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